Lithography is a commonly used technique for etching a desired pattern into a substrate, such as a semiconductor device. Typically, the substrate to be etched is secured into place with a securing device opposite a radiation source. A lithography mask is mounted between the radiation source and the substrate. The lithography mask is formed of a material that is opaque to radiation produced by the source but includes a radiation-transparent window with an opaque pattern. When the radiation source is activated, radiation emitted therefrom travels through the transparent portions of the window to the substrate but is prevented from passing through the opaque portions. A photoresist on the substrate is exposed in the desired pattern by the radiation passing through the transparent portions of the mask window. The photoresist is then developed and then used as a mask to etch the substrate.
Generally, semiconductor wafers to be etched are mounted on the upper surface of a pedestal positioned within a processing chamber. The position of the wafer relative to the upper surface and the radiation source can be adjusted by lift pins that extend through the pedestal body. The pedestal body also typically includes a cooling gas flow passage having an outlet positioned at the center of the pedestal upper surface. Helium is supplied to the passage for cooling the mounted wafer. This cooling prevents a photoresist layer on the wafer from burning due to high frequency voltage applied to the pedestal during exposure to the radiation and etching.
Typically, an elastomeric sealing ring is fixed on the circumferential edge of the upper surface of the pedestal. The sealing ring provides a seal between the bottom of the wafer and the upper surface of the pedestal. The sealing ring is usually V-shaped in cross-section, with the legs and vertex of the "V" fitting within an angled recess in the circumferential edge of the pedestal upper surface. With the sealing ring in place in the recess, one leg thereof projects above the upper surface of the pedestal and contacts the bottom surface of the wafer.
Unfortunately, during processing the sealing ring may adhere to the bottom of the wafer, as its surface contacting the wafer can melt due to the wafer's elevated processing temperature. When such melting occurs, lifting of the wafer by the lift pins also lifts the sealing ring and pulls it from the pedestal recess. This action can result in processing defects due to the leak formed between the sealing ring and the pedestal recess.
In addition, the sealing ring is typically formed of an elastomer having a Rockwell A hardness of 80A. This value is the result of more than 15 percent of the elastomeric material comprising inorganic filler added to reduce the material cost. Because of the presence of the filler, the elasticity of the material is reduced. The drop in elasticity can cause the sealing ring to deform during insertion on the pedestal which can, in turn, increase the chance of the sealing ring being unable to provide a seal.